The present invention relates to turbomachinery and more particular to a variable nozzle vane assembly upstream of the turbine.
In turbomachinery in which the turbine is intended to drive a compressor or the like, it is often desirable to control the flow of motive gas to the turbine to improve its efficiency or operational range. In order to accomplish this, the nozzle passageways leading to the turbine wheel may be of variable geometry. These variable geometry nozzle passages can be provided by means of a plurality of vanes which are pivotable so as to alter the configuration of the passages therebetween. However, with these pivotable vanes it is necessary to adequately seal the free ends of the vanes so as to avoid leakage of exhaust gas around the tips of the vanes. The leakage problem is particularly acute in high temperature engines where the relative radial displacement due to the thermal expansion is excessive between the inner shroud and the vane tips. Furthermore, sealing the vane tips against leakage must be accomplished in such a manner as to avoid binding of the vanes within the passageway.
Several different approaches have been taken in an attempt to provide an effective seal at the tips of the turbine nozzle vanes. One approach has been to springload the nozzle ring so that the vanes are always firmly held against the opposing wall, U.S. Pat. No. 3,112,096. Another approach involves the use of the pressure of the exhaust gas to load a pressure plate located within the outer shroud wall, against the vane tips, see U.S. Pat. No. 3,033,519. A third approach has been to allow exhaust gas pressure to force blades internal to the vane to extend from the vane in order to seal off any leakage pressure around the vane, see U.S. Pat. No. 3,101,926.